.mask{
 position: absolute;
 z-index: 1;
 top: 0px;
 left: 0px;
 width: 100%;
 height: 100%;
 background: rgba(0, 0, 0, 0.5);
 display: flex;
 justify-content: center;
 align-items: center;
}

.dialog{
 width: 300px;
 height: 300px;
 background: white;
}